CA1206262A

CA1206262A - Process and apparatus for strip flatness and tension measurements

Info

Publication number: CA1206262A
Application number: CA000462681A
Authority: CA
Inventors: Yu-Wen Hsu
Original assignee: Kaiser Aluminum and Chemical Corp
Current assignee: Kaiser Aluminum and Chemical Corp
Priority date: 1983-09-30
Filing date: 1984-09-07
Publication date: 1986-06-17
Also published as: DE3479096D1; EP0138430A2; ATE44894T1; AU560409B2; JPH0697167B2; EP0138430A3; US4512170A; EP0138430B1; JPS6093912A; AU3281784A

Abstract

TITLE OF THE INVENTION

PROCESS AND APPARATUS FOR STRIP FLATNESS
AND TENSION MEASUREMENTS

ABSTRACT OF THE DISCLOSURE

A process and apparatus for on-line measure-ment of unflatness of hot or cold rolled strip products, wherein the longidudinal bending of a shape roll over which the strip passes provides a measure of the un-flatness of the strip. Actual values of force, dis-placement or bending moment near the ends of the shape roll may be compared to theoretically predicted values for a flat product and for product having various out-of-flatness conditions. Preferably, the shape roll is supported at its ends by two pairs of supports, an the measurements at the supports are used in determining roll bending and thence strip unflatness. Other condi-tions such as off-center strip and asymmetric opera-tion of the rolling mill may also be determined from the measurement.

Description

BACKGROUND OF THE INVENTION

This invention relates generally to metal deforming operations~ and, more particularlyt to a process and apparatus for measuring unflatness of strip in a rolling mill.
Strip products of mat~rials such as aluminum are typically manufactured by passing thick pieces of the material through a rolling mill. It is highly desirable that the rolled strip be flat over its entire length and width, and not have excessive residual stresses which would cause it to buckle, as such imper-fections may ~ause the strip to break and may reduce fabricability in subsequent forming operationsO Flat-ness and residual stress imperfections arise from a variety of causes, such as a roiling mill which is not level or has excessive dimensional variations along i~s axis, plugged coolant spray nozzles, tension asymmetriesr and other causes which may be corrected by the mill operator or a process computer if the problem can be detected and recognized even as the rolling progresses. To this end, various types of on-line measuring equipment have been devised for monitoring a strip as it exits from the rolling mill.
Standard tensiometer rolls having a single pair of instrumented supports are commonly found in rolling mills. Such single-support tensiometer rolls can measure the total force and side-to-side differen-tial force exerted by the strip on the roll, but not various other conditions of imperfect rolling, such as unflatness. For the latter condition, several methods of measurement have been proposed~ including a series of commonly supported, laterally adjacent rollers which allow measurement of the strip tension at a series of points across the width of the rollO In another varia-tion, coaxial rollers having a plurality of internal load cells similarly provide information concerning thedistribution of strip tension across the width of the strip. From the distribution of strip tension, con-clusions can be drawn about the flatness of the strip.
In an alternative approach~ photocells or other non-contact proximity sensors may be used to detect the flatness5 thickness, or residual stress.
All of the previously proposed on-line flat-ness measurement processes and apparatus suffer from the10 common problem of extreme complexity and high mainten-ance cost. Some of the existing flatness measurementapparatus use a segmented roll body which may be the source of undesirable marking of the strip. Further, high capital investment costs are usually associated with such complex machines. Calibration of ~he multiple sensors or load cells typically involved in such ap-paratus is a continuing problem, particularly with apparatus employing pho~ocells. In most instances, the complex apparatus is not usable in hot rolling opera-tions because the measuring devices must be positioned too closely to the strip to be properly cooled.
Accordin~ly, there has been a continuing need for a less complex process and apparatus to detectmechanically induced rolling imperfections such as out-of flatness conditions. Such apparatus should be highly reliable and easy to main~ain, and be capable o~
detectin~ commonly occurring rolling problems. Prefer-ably, such apparatus would be based upon a standard piece of apparatus already available in most strip rolling mills~ so that capital investment cos~s and duplication of function would be minimized. The present invention fulfills this need, and further provides related advantages.

SUMMARY OF THE INVENTION

The present invention resides in a process and apparatus for detecting flatness variations and other mechanical imperfections arising in the rolling of strip products, wherein a roll or its support struc-ture is instrumented to permit determination of the load distribution imposed by the strip on the roll bOdyg from measurements of reaction characteristics such as force, displacement, or bending moment, preferably made at sensing positicns located near the ends of the roll.
When the roll is used as a shape roll, it performs the functions of a standard tensiometer as well as those of flatness measurement~ is reliable and easy to maintain, and may be used to monitor hot rolling processes because the instrumentation is positioned remotely from the working surface in contact with the hot metal.
In accordance with the invention, the appara-tus includes means for determining mechanical imper-fections of the strip from the longitudinal bending of the roll body under the load imposed by the strip as it passes over the roll, using measurements of reaction characteristics preferably m~de at sensing positions near the ends of the roll. Desirably, the roll is supported at its ends by two pairs of instrumented 2S supports, and the data gathered at these sensing posi-tions i5 used to deduce the presence of out-of-flatness and other mechanical imperfections of the strip passing over the roll. The measurements at the supports are compared with those predicted theoretically for a flat strip and various configurations of unfl~t strips~ and the condition of the strip is thereby determined from the support measurementsO
The present invention also extends to a process for determining mechanical imperfections of the strip from the longitudinal bending of the roll body ~2~

under the load imposed by the strip as it passes over the roll, using measurements of reaction characteristics preferably made at sensing positions near the ends of the rollO Desirably, reaction characteristics are measured at two oppositely disposed pairs of sensing positions adjacent the opposite ends of the rolll These measured reaction characteristics are compared with those predicted theoretically for a flat strip and variou~ configurations of unflat strips~ and the condi-tion of the strip is thence determined from the support measurements.
More specifically, there are several kinds ofcommonly occurring mechanical rolling defects~ such as center buckles and edge waves. Utilizing elastic beam theory, the reaction characteristics expected at the sensing positions can be calculated for such mechanical rolling imperfections, and then the actual measured values may be compared with the expected values.
Variations in the total forces between the two ends of the shape roll indicate asymmetric loading of the roll by the s~rip, which in turn may be related to a variety of problems. Other kinds of imperfections may further be detected from the reaction characteristics measured at the two pairs of ~ensing locationsO
It will be appreciated from the foregoing that the present invention represents a significant advance in the measurement of mechanical rolling im-perfections as strip products are being rolled.
The preferred apparatus and process utilize the well-proven technology of supporting a measurement roll through instrumented bearing supports on the roll neckof the roll~ well separated from the roll body which actually contacts the strip material. In the preferred embodiment, -the total strip tension and side-to~side strip tension variation may be determined as with a conventional tensiometer roll. The addition of a ~ o ~ ~
~z~ æ

second set of instrumented bearing supports, and the processin~ of their measured forces in conjunction with the forces on the first pair of bearing supports, allows determination of the most commonly occurring rolling defects, in either hot rolling or cold rolling opera tions~ Other features and advantages of the present invention will become apparent from the following more detailed description of the preferre~ embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
, FIGURE 1 presents perspective views of two metal strips, illustrating commonly occurring rolling defects; FIGURE lA illustrates an edge wave, and FIGURE
lB illustrates a center buckle;
FIGURE 2 is a schematic front elevational view of a dual support shape roll for flatness measurement, with an indication of the loaciing pattern resulting from a strip having the center buck;le of FIGURE lB;
FIGURE 3 is a side elevational view of a strip rolling mill with an on-line dual support shape roll installed therein;
FIGURE 4 is an enlarged, partially sectional front elevational view of the dual support shape roll for flatness measurement;
FIGURE 5 is an enlargedy partially se~tional, side elevational view of the shape roll, taken general-ly along line 5-5 of FIGURE 4; and E`IGURE 6 is an enlarged, partially sectional top plan view of the shape roll, taken generally alony line 6 6 of FIGURE 5O

o7--DETAILED DESCRIPTION OF T~E PREFERRED EMBODIMENT

As is shown in the drawings for purposes of illustrationt the present invention is embodied in a dual support shape roll 10 for detecting and measuring mechanical imperfections, such as those illustrated in FIGURE l, in a rolled s~rip 12, as well as for measuring strip tension of the strip 12 as it is being rolled.
The dual support shape roll 10 is placed on-line with a rolling mill stand on the exit side of the millO The strip emerging from the rolling mill passes over a roll body 14 of the dual support shape roll 10, whereby rolling defects and strip tension are determined from measurements of the forces on two pairs of instrumented supportsO While the preferred embodiment of the inven-tion is cle~cribed in terms of a shape roll placed on theexit side of the mill~ those skilled in the art will recognize that the invention may be applied in other contexts~ such as, for example, instrumented work rolls or a shape roll placed between roll stands of a multi-stand mill.
In accordance with a preferred embodiment ofthe invention, the roll body 14 of the dual support shape roll lO is supported by two pairs of instrumented supports comprising sensing positions, rather than by a single pair of instrumented supports as found in conven-tional tenslometers. Each of the four supports i5 instrumented to measure its respective reaction char-acteristie as the strip 12 passes over the roll body 14 in tension~ As used herein; ~he term "reaction char-acteristic" means the response of the sensing positionto the forces imposed on the roll body 14 by the strip 12 t and typically the reaction characteristic may be either the force, displacement or bending moment measured at the sensing position. Most conveniently;
the reaction characteristic is measured with a load cell positioned between the support and the frame of the machine. By measuring and then analyzing the reaction characteristics of the four supports, the total strip tension, side-to-side differential strip tension and strip tension distribution across the width associated with strip unflatness may be detected. The term "strip"
as used herein denotes strip, sheet, and other generally flat products which may be measured by the dual support shape roll. A "sensing position" is a location whereat a measurement of a reaction characteristic is taken~ and is preferably but not necessarily a load-carrying support structure. Finally, the preerred apparatus is referred to herein as a "dual support 1I shape roll. The term "dual support'~ relates to the use of two pairs of supportsO
A schematic form of one preferred embodiment o the invention is illustrated in FIGURE 2. The cylindrical roll body 14 has a pair of roll necks 16 and 18 extending from either end thereof, along the cylind-rical axis of the roll body 14L. The primary support for the roll body 14 and the strip 12 passing thereover isprovided by a pair of inner bearings, including a first inner bearing 20 and a second inner bearing 22. The pair of inner bearings 20 and 22 are disposed at the opposite ends of the roll body 14 and receive the respective roll necks 16 and 18 therein, thereby provid-ing the primary support structure for carrying the weight of the dual support shape roll 10 and the force of the strip 12 pressing downwardly on the roll body 14~ ~he inner bearings 20 and 22 are in turn respec-tively supported by a pair of load cells~ including a first inner load cell 24 and a second inner load cell A pair of outer bearings, including a first outer bearing 28 and a second outer bearing 30, are also disposed at the opposite ends of the roll body 14 and receive the roll necks 16 and 18 therein, but the outer bearings 28 and 30 are positioned on the roll necks 1~
and 18 at locations further outwardly from the respec-tive inner bearings 20 and 22. The outer bearings 28 and 30 are supported by a first outer load cell 32 and a second outer load cell 34, respectively. As will be described more fully hereinbelow, the strip ten~icn and presence of misalignment or mechanical imperfections may be determined from measurements of the four load cells 24, 26, 32, and 34. While measurement of four load cells is preferred, the measurements could be taken from only three sensing positions, at least two of which are oppositely disposed at the ends of the roll body.
FIGURE 3 illustrates the usual manner of positioning and use of the dual support shape roll 10 lS on-line in a rolling mill. The strip 12 is thinned by passing it between a pair of work rolls 36. A pair of back-up rolls 38 may be provicled to minimize longitudin-al bendi.ng of the work rolls 36, which would result in a thickness variation across the width of the strip 12.
In the view of FIGURE 3, the strip 12 is driven through the work rolls 36 from left to right under a strip ten sion indicated schematically by the letter T.
To determine the presence of misalignment and mechanical imperfections in the rolled strip, as well as the strip tension T, the dual support shape roll 10 i5 positioned on the exit side of the work rolls 36, a~d disposed so as to displace the strip 12 upwardly and out of the plane that it would otherwise assume under the strip tension T. An idler roll 40 contacts the upper side o~ the strip 12 at a location yet further from the work rolls 36 than the dual support shape roll 10, forcing the strip 12 downwardly against the dual support ~hape roll 10. A wrap angle D may be defined as the angle between the segment of strip 12 lying between the work roll 36 and the shape roll 10, and the segment oE strip 12 lying between the shape roll 10 and ~he idler roll 40~
When the rolling mill is level and the s~rip 12 is properly centered on the roll body 14~ the down-ward force of the strip 12 on the roll body 14 is evenlydistributed, so that the forces measured by the two inner load cells 24 and 26 are substantially identical to each other, and the forces measured by the two outer load cells 32 and 34 are substantially identical to each other. If the work rolls 36 are not level or the strip 12 is displaced sideways from the longitudinal center of the roll body 14, the force measured by one of the inner load cells 24 and 26 will be greater than that measured by the other. When this condition is detected, the rolling mill must be leveled or the strip 12 centered on the roll body 14 through suitable mill adjustmentsO As used herein, a "level" rolling mill is one having a gap between the work rolls that is symmetrical about the longitudinal center of the work rolls. In the analysis next presented, it will be assumed that such adjustments have been made, so that the rolling mill is level and the strip 12 is centered on thle roll body 14.
To relate the distribution of loads on the roll body to reaction characteristics at the sensing positions, the roll body 14 and roll necks 16 and 18 of the dual support shape roll 10 may be modeled as an e~astic ~eam carrying a distributed load across a portion of its center section, and elastically supported by two pairs of supports of ~nown stiffness. Based upon this general premise, various approaches may be taken to predict the dependence of the loading on the two pairs of supports as a function of the load variation across the width of the strip 12. In the presently preferred analytical approach, the downward force per unit width variation across the width of the strip 12 is assumed to be approximated by the parabolic form:

~11-Load = W(l- ~(1-12 X2)) (1) In this assumed functional dependence of the loadl the single parameter a describes the shape of the load distribution If ~ is zero, the load is evenly dis-tributed across the width of the strip 12. However,where ~ is greater than zero, the load distribution is a concave parabola as illustrated in FIGURE 2, which corresponds to a center buckle mechanical imperfection (as illustrated in FIGURE lB)~ Conversely, when ~ is less than zeror the load pattern is a convex parabola corresponding to an edge wave (not illustrated in FIGURE

2, but corresponding to a defect of the type illustrated in FIGURE lA~ Other constants required or the analy~
sis of the roll body 14 under a distributed load are also illustrated in FIGURE 2, where:

W is the width of the sheet 11, 12, and 13 are the indicated dimen-sions F is the algebraic sum of the forces on the four supports Ki is the spring constant for each of the pair of inner supports K is the sprins constant ~or each of the pair o outer supports EIl, EI2, and EI3 are bending rigidities of the indicated sections X is the linear dimension from the center of the roll body The bearing reaction force R measured by each of the outer load cells 32 and 34 may be calculated by applying the principles of elastici.ty to an ela~tically supported beam carried by four supports, and bearing a ~a2~6~
~12-distributed load of the functional form of equation (1), with the following result:

R , A2 ~ (21 )2 (6 ~ l5 ~B. (2) A and B are constants of the form:

A = 2 3 2 2 3 i_ i CO ~ a3(r2 ~ 1/3 r3a3 -~ a ) B = _ 1/2 r2a3 Ci + ~ ~ a31r2 + 1/3r3a3 + a2j witA

Ci ~ cO = ~

EI2 E~2 r2 EIl r3 EI3 a2 11 13 Accordiny to this result, the outer bearing reaction force R is dependent upon the shape para-meter ~ , the sum of the forces F 9 and known roll and strip constants. Equation 2 may be solved for the shape parameter a from measurements taken on either of, or preferably, the average of, the readings of th~ outer load cells 32 or 34, and the net resultant force from measurements o all four load cells 24, 26r 32, and 34O In effect, such a solution compares the predicted and measured val.ues o~ the reaction characteristic until the values match at the appropriate value of ~ .

,.io 2~

~ may be negative, corresponding to an edge wave;
positlve, corresponding to a center buckle; or zero, corresponding to a flat sheet. Where ~ is not zero, a corresponding correction signal may be sent to the rolling mill operator or control system. The objective of this control signal is to reduce the absolute value of ~ to substantially zero, and the control system can monitor the success of the control signal in achiPving this objective.
It is emphasized that the scope of this invention is not to be limited by the specific model or parameters described in the preceding analysis leading to Equation 2, inasmuch as a variety of different models may be devised based upon a dual support shape roll designO Further, such models may not be confined to measurements of loading, but instead may be directed to measurements of displacement o portions of the roll, bending moments, or any other measurement providing a reaction characteristic as a function of load distribu~
tion. Measurement of ~orces by load cells is preferred, since such instrumentation is reliable and may be obtained commercially. Further, as indicated pre-vio~sly9 the strip tension T may be directly calcu-lated from the algebraic sum of the load cell measure-ments as:
V-~ (3) T _ ~_ 2 V is the average load reading of the inner load cells and D is the strip wrap angle.

A most preferred structure of the dual support shape roll 10 is illustrated in FIGURES 4-6 for one end of the roll body 14. In this most preferred embodiment/
the two supports at each end of the roll body 14 are ..~

~iL2~

~14-enclosed in a common housing~ with the housirlg supported by a load cell 25 termed herein a "tension" load cell.
This design has practical construction advantages, as discussed hereinbelowO Additionally, it allows the force on the ~ension load cells 25 to be used as a measure of strip tension T, and the force on a flatness load cell 33 at the end of the roll neck to be used as a measure of unflatness.
The roll neck 16 includes first and second roll neck portions 42 and 44 respectively, extending axially from the cylindrical roll body 140 The first roll neck portion 42 is of larger diameter and extends through the inner bearing 20. The second roll neck portion 44 is of lesser diameter, and extends through the outer bearing 28. Inasmuch as the inner bearing 20 carries the majority of the weight of the roll boay 14 and the forces imposed by the strip 12 passing o~er the roll body 14 and also should be free of resistance to bending rotation~ it is preferably of a spherical roller bearing type. The outer bearing 28 carries a lesser load, and îs preferably of the ball bearing type.
The inner bearing 20 is supported by a pivot plate 4~, which in turn is free to pivot abo~t a fixed point in its supporting structure. The pivot movement allows vertical movement of the roll assembly but prevents sideways movement, thereby preventing damage to the load cells, which are suscep~ible to damage by sideways loading. A pivot plate support pin 48 passes horizontally through a hole near one end of the pivot plate 46. Pivot plate bearings 50 allow the pivot plate support pin 48 to pivot about a pivot support base 52. The pivot plate 46, the inner bearing 20~ and the roll body 14 are thereby permitted to pivot about a generally horiæontal axis parallel to, and at substantially the same height as~ the axis of the roll body 14~

~2d:~62~2 The end 54 of the pivot plate 46 remote from the pivot plate support pin 48 rests upon, and is supported by, the tension load cell 25, which in turn rests upon a base 56. The dead weight supported by the tension load cell 25 is electronically subtracted from the force signal so that the downward component of the force exerted by the strip 12 as it passes over the roll body 14 is directly available for further analysis.
In the preferred embodiment, the ou~er bearing 28 is mounted to a pivot arm 58, which in turn is mounted to the pivot plate 46 by a pivot arm pin 60 which projects through a hol~ in the end 62 of the pivot arm 58 remote from the outer bearing 28. The pivot arm pin 60 is pivotably received in the pivot plate 46, with a pair of pivot arm bearings 64 provided to allow the pivot arm 58 to pivot freely. The pivot movement prevents undue sideways loadings, as previously dis-cussed~
The flatness load cell 33 is interposed between the end of the pivot arm 58 adjacent the outer bearing 28, and the pivot plate 46 to measure the force at the outer bearing 28. In one example wherein the roll body 14 is a five-inch diameter hardened steel roll, the ten~ion load cell 25 is selected to have a ~5 1000 lb~ capacity, while the flatness load cell 33 is selected to have a 500 lb. capacity.
Other aspects o the mechanical construction and assembly of the preferred dual support shape roll illustrated in FIGURES 4-6 are within the skill of those in the art.
The dual support shape roll in accordance with the invention is installed on-line in a rolling mill in the manner illustrated in FIGURE 3. The height of the roll body 14 i5 adjusted so as to force the strip 12 upwardly to produce a wrap angle D of about 7-9 , or o~herwise as may be necessary so that the load on the tension load cell 25 does not exceed its capacity.
The dual support shape roll of the present invention must be calibrated before startup. Prefer-ably, such calibration is performed off-line using dead loading. In the initial design of the shape roll, calculated values of constants such as A and 8 in equation ~ are used, and the off-line calibration yields the exact values for use in subsequent operations. In the dead loading calibration, various loading conditions are simulated by applying weights to the roll body and measuring the forces on the load cells. From these measurements 9 corrected constan~ values are determined for use in the on-line operations.
During the rolling process, the forces meas-ured by the four load cells are monitored. Frcm thetotal roll force F, the total strip tension T may be calculated by equation 3 (with V-R replaced by the average forces measured by the two tension load cells 25). The value of ~ is calculated from the load cell measurements and the constants~ using equation 2.
Alternatively, the quantity R/F may be continuously calculated or monitored and if the value deviates from that corresponding to ~ equal to ~ero, an out-of flat~
ness condition is signal1ed. If the value of R/F falls below that corresponding to ~ equal to zero, the value of ~ is positive and a center buckle condition is present. Conversely, if the value of R/F rises above that corresponding to ~ equal to zero, the measured value of ~ is negative and an edge wave condition is present. Whatever the method usedr the out-of-flatness condition signal may then be communicated to the rolling mill operator for manual adjustment of the mill, or to automatic equipment for adjustment of the mill.
~uring production operations, the force values measured by the two tension load cells 25 should remain substantially eqLIal to each other~ and the forces ~2Ci6Zt~2 measured by the two flatness load cells 33 should remain substantially equal to each other. If this condition is not satisfied, asymmetry of the rolling operation is indicat~d. Possible causes of the asymmetry include out-of-parallel work rolls 36, wandering of the strip 12 to one side of the center line of the roll body 14, a condition of asymmetric unflatness, or a mechanical malfunctioning of the rolling mill such as plugged coolant spray nozzles on one side of the mill. The out-of-symmetry indica~ion does not identify the cause of the asymmetry, but instead serves only as a warning of the condition, which may then be investigated by the operator.
In the preferred mode of operation, the two tension load cells 25 are constantly monitored and maintained at substantially equal force values by adjustment of the levelness of the mill through control of the gap between the work rolls 36. The two flatness load cells 33 are used to determine strip unflatness using equation 2. If the two tension load cells 25 indicate substantially e~ual forces while the two bending load cells 33 are significantly different, an asymmetric flatness condition, possibly due to one of the aforementioned causes, is signalled to the operator or control computer.
Some types of local flatness disturbances such as trap buckles are not directly detected by the dual support shape roll of the present invention.
However, in many applications such minor, localized disturbances are not critical for the rolling process, including all instances of hot rolling, and multi-stand cold rolling except for the exit stand. Use of a proper coolant spray pattern would minimize such localized unflatness.
Although the preferred embodiment has been discussed as a dual support shape roll wherein the 6~

sensing positions correspond to the supports, those skilled in the art will recognize that other approaches ~o measurement of longitudinal bending are within the scope of the present invention. For example, the displacement o~ a sensing position may be measured by non-contact means at the roll necks or on the roll body. Further, the measurements of reaction character-istics may be of mixed type, for example, force measure-ments of a pair of supports and displacement measure-ments at the other sensing positionsO
It will now be appreciated that, through theuse of the process and dual support shape roll appara-tus of this invention, measurements of strip tension and unflatness may be readily made. The apparatus is reliable, easily maintained, and o relatively low capital costs as compared with other on-line methods of determining strip unflatness. The relatively low capital cost allows placing of a shape roll after each stand of a multistand rolling operationO Moreover, the preferred dual support shape roll may be utilized to monitor flatness in single-stand or multistand hot rolling operations, as the load cells are positioned remotely from the hot strip and may be adequately protected frvm the heat.
Although a particular embodiment of the invention has been described in detail for purposes of illustration, various modifications may be made without departing from the spirit and scope of the invention~
Accordingly, the invention is not to be limited except as by the appended claims.

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for monitoring a continuously moving metal strip in a rolling mill comprising the steps of selecting a first and second pair of load-sensing pos-itions, continuously supporting the moving strip under tension on an endless unitary surface rotatable about an axis and intermediate the first and second pair of load sensing positions with the individual positions of a given pair being located at a different end of said axis and the locations of the positions of one pair of load-sensing positions being disposed in opposed relationship on an opposite side of said axis with respect to the other pair of load-sensing positions, continuously and simultaneously measuring a reaction characteristic for at least three of the load-sensing positions relative to theoretically calculated flat strip values and continu-ously making determinations of the unflatness of the strip from the measured reaction characteristics.

2. The process of claim 1 wherein the re-action characteristic comprises a bending force and the determination of the unflatness of the strip includes the steps of ascertaining a load-sensing position bending force corresponding to a loading pattern on the endless surface for a given one of the load-sensing positions and comparing the ascertained and measured load-sensing position bending force with the position force which has been previously theoretically calculated for said given load-sensing position for rolling flat strip to determine the loading pattern on the endless surface.

3. The process of claim 1 including the step of disposing the load-sensing positions of one of the said pairs of positions outwardly of the positions of the other pair of positions.

4. The process of claim 2 wherein the load-sensing position whose bending force is measured is one selected from the second pair of load-sensing positions and said second load-sensing position pair comprising flatness-sensing positions.

5. The process of claim 1 wherein at least two of the sensing positions from said pairs of sensing positions are located in areas where a portion of the weight of the endless surface is supported.

6. The process of claim 1 wherein the reaction characteristic comprises a deflection of a load sensing position and said unflatness determination includes the further steps of measuring and ascertaining a calculated endless surface reflection corresponding to a loading pat-tern on the endless surface for one of the load-sensing positions of said first pair of load-sensing positions and then comparing the measured load-sensing position de-flection to the calculated load-sensing position deflec-tion theoretically calculated for a flat strip in order to determine the loading pattern on the endless surface.

7. The process of claim 1 wherein the reaction characteristic is a bending moment and said unflatness determination includes the steps of ascertaining a calcu-lated load-sensing position bending moment corresponding to a loading pattern on the endless surface for the first-mentioned pair of load-sensing positions and then compar-ing the measured sensing positions bending moment to the theoretically calculated bending moment for the load-sensing positions to determine the loading on the endless surface.

8. The process of claim 1 including the further step of adjusting the rolling mill to eliminate the unflatness that is ascertained in said determination step.

9. An apparatus for measuring flatness of a length of metallic strip comprising a roll rotatable about a longitudinal axis and having a unitary body por-tion for supporting the strip, a first pair of load-sensing elements with the individual elements thereof be-ing disposed at opposite ends of said roll, a second pair of load-sensing elements wherein the individual elements thereof are also disposed at the opposite ends of said roll, and in opposed relationship on opposite sides of said axis with respect to the load-sensing elements of said first pair of load-sensing elements, and said load-sensing elements being preset to simultaneously measure the reaction characteristics for at least three of said load-sensing elements relative to those theoretically calculated for flat strip.

10. The apparatus of claim 9 including bearing supports for said roll and at least two of said load-sensing elements being loaded adjacent the roll-bearing supports.

11. The apparatus of claim 9 including means mounting the ends of said roll so as to prevent sideways movement of said load-sensing elements.

12. The apparatus of claim 10 including means mounting the ends of said roll to prevent sideways move-ment of said load-sensing elements.

13. The apparatus of claim 11 wherein said last-mentioned means comprises pivot plates for said roll end mounting means.

14. The apparatus of claim 12 wherein said last-mentioned means comprises pivot plates for said roll end mounting means.

15. The apparatus of claim 9 wherein the oppos-ing pairs of load-sensing elements are located on opposite sides of the longitudinal axis of the roll.

16. The apparatus of claim 11 wherein the opposing pairs of load-sensing elements are located on opposite sides of the longitudinal axis of the roll.

17. The apparatus of claim 9 wherein the load-sensing elements of said second pair of elements are located outwardly of the elements in said first pair of elements.

18. A dual-support shape roll, comprising:
a roll having a cylindrical roll body for supporting a length of strip and a pair of roll necks for supporting the roll body extending axially from the roll body along the cylindrical axis thereof;
a pair of inner bearings at the opposite ends of said roll and receiving the respective roll necks therein;
a pair of pivot plates at the opposite ends of said roll, said pivot plates having means for respectively mounting said pair of inner bearings;
first pivot means for pivotably supporting said pivot plates to allow said pivot plates to pivot about an axis parallel to the axis of said cylindrical roll;
a pair of tension load cells in contact with said pivot plates to measure the respective loads imposed thereon;
a pair of outer bearings at the opposite ends of said roll and receiving the respective roll necks therein, each of said pair of outer bearings being disposed fur-ther from said roll body than the respective inner bearings;
a pair of pivot arms at the opposite ends of said roll, said pivot arms having means for respectively mounting said pair of outer bearings;

second pivot means for pivotably supporting said pivot arms on the respective said pivot plates to allow said pivot arms to pivot about an axis parallel to the axis of said cylindrical roll; and a pair of flatness load cells in contact with said pivot arms to measure the respective bending loads imposed upon said outer bearings.